The technology of High Speed Uplink Packet Access (HSUPA) introduced in the 3GPP R7 as an uplink enhanced solution is intended to improve the uplink peak rate of a user and the throughput of a system.
A series of enhanced channels and corresponding data transmission mechanisms have been introduced in the technology of High Speed Uplink Packet Access (HSUPA): when a User Equipment (UE) intended to transmit uplink Enhanced Dedicated Channel (E-DCH) data, Scheduling Information (SI) will be transmitted to a base station over an E-DCH Random Access Uplink Control Channel (E-RUCCH) or an Enhanced Uplink Physical Channel (E-PUCH) to signal the amount of currently buffered data of the UE and other relevant information to the base station. Particularly if the UE has a granted resource, then the UE carries the SI information in an MAC-e PDU and transmits it to the base station over the E-PUCH channel; on the contrary, if the UE has no granted resource, then the UE has to transmit the SI information to the base station over the E-RUCCH channel. Next the base station grants a physical resource available to the UE over an E-DCH Absolute Grant Channel (E-AGCH); and thereafter the UE transmits uplink enhanced service data over an E-DCH Physical Uplink Channel (E-PUCH); and finally the base station feeds back ACK/NACK information to the UE over an uplink enhanced acknowledgement indicator channel.
In the 3GPP R8, the enhanced feature of CELL_FACH has also been introduced for a TD-SCDMA system by introducing the status of CELL_FACH to an HSPA resource (including HSUPA and HSDPA-related transport and physical channels) and a corresponding transport mechanism so that the features of HSUPA and HSDPA have to be supported to accommodate a CELL_FACH enhancement requirement. A UE is allowed in the enhanced status of CELL_FACH to be out of uplink synchronization, so when a base station has downlink data to be transmitted to a UE, the base station detects the UE out of uplink synchronization based upon a timer and initiates a UE uplink resynchronization process for the UE out of uplink synchronization by firstly instructs in an HS-SCCH command (downlink physical layer control signaling) the UE to initiate the uplink synchronization process; and the UE transmits an E-RUCCH to the base station to acknowledge finished synchronization after transmitting an SYNC_UL, receiving an FAPCH and performing successful uplink synchronization upon reception of the synchronization command, and then the base station transmits downlink data. It shall be noted that the E-RUCCH has not been structurally changed with CELL_FACH enhancement, that is, information borne over the E-RUCCH has not been changed relative to an HSUPA, so SI information is also borne over the E-RUCCH.
Furthermore, a user equipment with CELL_FACH enhancement transmits data over an E-DCH in the uplink and receives data over a High-Speed Downlink Shared Channel (HS-DSCH) in the downlink. With an improved peak rate of data, if the UE stills reselects a cell by itself without signaling to a network, the period of a system message typically may be up to 1.28 s, and only after the UE reads a system broadcast upon reselection of a cell, the UE can transmit a cell update message in the new cell and the specific cell where the UE resides can be known to the network side, then it is unknown to the network whether the UE has reselected any cell before the UE reselects the new cell, that is, before the network receives the updated cell, and if a base station continues with scheduling the UE, then the problems of a waste of resources and a possible loss of data may arise, and a cell reselection indicator process has been proposed to address the problems.
Specifically, in the cell reselection indicator process, the UE performs a cell reselection criterion; and after a cell reselection condition is satisfied, the UE judges whether a cell reselection indicator transmission condition is satisfied, and if it is satisfied, then the UE transmits a cell reselection indicator to the base station and reselects a cell after transmitting the cell reselection indicator. Particularly in the process of transmitting the cell reselection indicator, for uplink data transmission, if the UE transmits information of TEBS>0 but not TEBS=0 to the base station, then the cell reselection indicator transmission condition is triggered; and then the UE judges if there is a grant in a next Transmission Time Interval (TTI) or an extended estimation window, then the UE transmits the cell reselection indicator represented as TEBS=0 and HLBS=“1111” over an E-PUCH; or if there is E-PUCH grant in the next TTI or the extended window, then the UE initiates an E-RUCCH process by transmitting the cell reselection indicator represented as TEBS=0 and HLBS=“1111” to the base station. The largest number of synchronizations is set to 1 for transmission of the cell reselection indicator from the UE in the E-RUCCH process, and if the E-RUCCH process fails to be performed in a physical layer random access process, then the UE stops the cell reselection indicator from being transmitted and reselects a cell. For downlink data reception, if cell reselection is triggered during reception of downlink data, then the user equipment carries RTBS=0 as the cell reselection indicator over an HS-SICH. If there is uplink synchronization ongoing for the user equipment, then the user equipment carries and signals information of TEBS=0 and HLBS=“1111” in an E-RUCCH process to the base station.
As can be apparent from the foregoing description, the UE with uplink E-DCH data to be transmitted transmits the SI information to the base station over the E-RUCCH channel, and if the UE with the enhanced feature of CELL-FACH is out of uplink synchronization, then the UE also transmits the E-RUCCH to acknowledge finished synchronization upon reception of the synchronization command from the base station, but the E-RUCCH channel has not been changed relative to the HSUPA despite the CELL-FACH, and furthermore the UE may also initiate the E-RUCCH process to transmit the cell reselection indicator represented as SI information to the base station. Therefore if the UE has uplink E-DCH data to be transmitted and the UE also has downlink data to be transmitted while the UE out of uplink synchronization performs the cell reselection indicator process, then the base station may not know whether the E-RUCCH returned from the UE is to acknowledge finished synchronization, to transmit SI information to apply for a scheduling grant or to signal cell reselection upon reception of the E-RUCCH, which may disordering the processes of the base station and the UE.